Approximate efficiency of a linear regulator is given by the ratio of regulated output voltage to input voltage. Higher voltage difference between the input and the output means a lower efficiency due to heavy losses in the series power semiconductor. Supercapacitor-assisted low dropout regulator (SCALDO) is an emerging linear DC–DC converter technique, where a supercapacitor (SC) is used to reduce the voltage drop across the series transistor in a linear regulator where the SC acts as a lossless dropper. The circuit operates at a very low frequency decided by the size of the SC. An efficiency multiplication factor such as 1.33, 2, or 3 is achieved depending on the configuration. This study presents the essentials of its generalised theory, few prototype implementations, and a discussion on SCALDO properties. Typical efficiencies of 12–5 and 5–1.2 V linear regulators are around 42 and 24%, respectively. When SCALDO prototypes are built, the authors achieve respective end-to-end efficiencies of 79–81 and 58–73%. A loss analysis summary and further developments of the novel technique are also provided, in addition to a discussion to indicate that this is not a variation of the switched capacitor converters.

Hard-switching flyback converters are widely used in the low power application but suffer from high electromagnetic emissions, current ripples, and low efficiency. To overcome these problems, a half-bridge flyback converter with a new lossless passive snubber is proposed using an interleaved structure. All switches of the proposed converter turn on under zero current switching and turn off under zero voltage switching which decreases the switching losses and electromagnetic interference (EMI). Theoretical analysis of the proposed converter is presented and verified by the experimental results of a 200 W prototype. In addition to the 7% efficiency improvement, the proposed converter has lower EMI in comparison with its hard-switching converter.

Here, a highly efficient MOSFET neutral-point-clamped (M-NPC) transformerless inverter is proposed for photovoltaic (PV) applications. By employing super-junction metal–oxide–semiconductor field-effect transistor (SJ-MOSFET) as well as silicon carbide (SiC) diodes, high efficiency is achieved. Furthermore, the common-mode voltage (CMV) is completely clamped at half of the input voltage with clamping branch. Therefore, leakage current is eliminated. The performances of different topologies, in terms of CMV, leakage current, total harmonic distortion (THD), losses, and efficiency, are compared with the proposed M-NPC topology. The analyses are carried out theoretically via MATLAB/Simulink, and further validated with experimental tests. The experimental results show maximum efficiency of 98.5% and European efficiency of 97.65%.

DC/DC converters are crucial in DC distribution networks for converting voltage and interconnecting different voltage links. The modular multilevel high-frequency-link DC transformer (MDCT), which employs multiplex conversion principle and provides many advantages, realises voltage conversion, power transfer and electrical isolation between links in medium-voltage DC distribution networks. To improve the performance of MDCT, this study investigates the modulation with the phase-shift strategy and its influence on current stress, power characteristic and efficiency characteristic of MDCT. Besides, to simultaneously achieve an optimal solution for both current stress and efficiency characteristics of MDCT, an optimal modulation strategy based on dual-phase-shift is proposed. Finally, an MDCT prototype is constructed and experimental results verify the correctness and effectiveness of the analysis and proposed scheme.

Modern DC–DC resonant converters are normally built around a voltage-source series-resonant converter. This study aims to facilitate the practical use of current-source parallel-resonant converters due to their outstanding properties. To this end, this study presents a sliding-mode control scheme, which provides the following features to the closed-loop system: (i) high robustness to external disturbances and parameter variations and (ii) fast transient response during large and abrupt load changes. In addition, a design procedure for determining the values of the control parameters is presented. The theoretical contributions of this study are experimentally validated by selected tests on a laboratory prototype.

An improved high efficiency wide zero-voltage-switching (ZVS) range push–pull converter for low-voltage to high-voltage power conversion is proposed in this study. For this improved converter, all of primary switches are turned on with ZVS operation from full load to light load by using the energy stored in the leakage inductance aided by the magnetising inductance. The resonance between the leakage inductor and the voltage-doubler-rectifier capacitors reduces not only the voltage and current stresses of rectifier diodes but also the turns ratio of high-frequency transformer and conduction loss. In addition, the circulating energy is decreased dramatically compared with the similar converter resulting in lower conduction loss. This topology features simpler structure and higher efficiency. Detailed operational principle, design, comparative study and experimental results are fully discussed in the text. Finally, a 200 W experimental prototype has been built to verify the effectiveness of the proposed concept.

A four-level open-end winding induction motor drive (OEWIMD) is realised by feeding the open stator windings of a three-phase induction motor from either end with two-level voltage source inverters (VSIs). These VSIs are operated with unequal DC-link voltages, which are in the ratio of 2:1. This circuit configuration has the disadvantage of overcharging the DC-link capacitor of the inverter operated with the lower input voltage. Decoupled space vector pulse-width modulation (DSVPWM) schemes, which were suggested in the previous literature to circumvent this problem, result in higher switching power loss in the dual-inverter topology. It is known that the discontinuous pulse-width modulation (PWM) schemes reduce the switching power loss. However, lack of structural symmetry of the power circuit renders it unwieldy to devise these PWM schemes. This study explores the applicability of discontinuous decoupled SVPWM (DDPWM) techniques for the four-level OEWIMD, without compromising on the waveform symmetries. With the aid of an improvised loss model, it is shown that these PWM schemes achieve the reduction of the overall loss of the four-level OEWIMD compared to the DSVPWM schemes. It has also been observed that one of the proposed DDPWM schemes result in reduced dv⁄dt in the motor phase voltages.

In recent days, multilevel inverters are quite popular in the photovoltaic system to improve the power quality. One of the popular multilevel inverters for medium power applications is neutral point clamping inverter. However, with the limited number of switching combinations, energy balancing and fault-tolerant operation is a major issue. The absence of energy balance mechanism may lead to unequal charge and discharge patterns in the batteries used in off-grid applications, which in turn results in the un-equal voltage at the batteries terminals. The difference in voltage between the sources can introduce the DC voltage offset at AC output, which causes serious problems when fed to the transformers or inductive loads like the induction motor. To address this problem, a five-level inverter is proposed which is capable of energy balancing between the two DC sources, minimising the DC voltage offset and able to operate in some fault-tolerant conditions. At the same time, this topology uses less number of switches as compared to conventional three-phase five-level inverters. The proposed topology is developed by combining conventional two-level and three-level inverters. The topology is verified by simulation using Matlab Simulink and tested on a laboratory prototype. The control algorithm for prototype is implemented with the help of Xilinx SPARTAN-6 (XC6SLX9) FPGA board.

Recently, efficiency improvement of wireless power transfer (WPT) systems has been the focus of research. Conventional methods of DC–DC converters are employed for load modulation to achieve high efficiency over large variations in mutual inductance and load. However, these additional circuits degrade the performance due to their inherent losses. To address this problem, this study presents a dual-side phase shift control method for load modulation and voltage regulation in a compact WPT system. The key features of the proposed work are: attaining load modulation and voltage regulation with reduced size of the system; elimination of communication between active bridges and simple control logic. Mathematical expression of equivalent resistance versus the phase shift angles (PSAs) is deduced and the optimal PSAs for maximum efficiency are presented. Utilisation of local control, stability analysis and fault detection method are included. MATLAB/Simulink simulation and experimental results are carried out to validate the proposed method.

In a variable switching frequency control scheme, it is challenging to design the voltage source inverter (VSI) parameters without knowing the maximum and minimum switching frequencies. The switching frequency variation depends on the system parameters. Therefore, the expression for frequency variation in one inverter topology does not hold in other topologies. The design of hysteresis current controlled four-leg shunt active power filter (APF) requires the switching dynamics analysis to ensure satisfactory performance of the inverter. In this study, a detailed analysis on the switching dynamics of hysteresis current controlled four-leg VSI and design of various inverter components for compensating unbalanced and non-linear loads are presented. The results obtained from these analyses can be used in any applications involving hysteresis current controlled four-leg VSI. These results are supported by detailed simulation studies conducted on a three-phase four-leg shunt APF system using Matlab/Simulink. The theoretical studies and design of passive components are also verified by conducting experiments on a prototype of four-leg shunt APF developed in the laboratory.

An electrical method for junction temperature estimation of insulated-gate bipolar transistors (IGBTs) is presented in this study. Owing to the parasitic inductance between bond wire and main emitter terminal L _E. The temperature-dependent falling collector current during turn-off transition would cause a negative voltage drop in the gate-main emitter voltage waveform v _gE. Therefore, this negative voltage drop V _gE-np is proportional to the junction temperature. A double-pulse test circuit is developed to verify the accuracy and feasibility of the proposed method. The impacts of collector–emitter voltage V _ce, collector current I _c and bond-wires cut-off are also be discussed theoretically and experimentally. The experimental results show that the proposed V _gE-np has a linear relationship with junction temperature as theoretical analysis and it is a bond-wires cut-off independent parameter in some special test point, which offers an effective way to estimate junction temperature without package destruction. The advantages of the proposed method include good linearity, bond-wires failure immunity and adequate sensitivity with junction temperature.

A wind energy conversion system employing dq control has been proposed for extracting maximum power from a wind-driven permanent magnet synchronous generator (PMSG) and feeding it to a three-phase utility grid. The controller consists of a diode bridge rectifier, a dc–dc boost converter and a voltage source inverter (VSI). The grid synchronisation is achieved by controlling the VSI at the grid side. Besides supplying power to the ac grid, the proposed scheme also feeds a local dc load, as the dc link voltage is maintained constant. To evaluate the performance of proposed scheme, MATLAB/Simulink based model is tested under varying wind speeds. A proportional–integral controller is used for varying the duty ratio of the dc–dc converter to maintain the output dc voltage constant. The decoupled control algorithm for independent control of real and reactive power fed to the grid is implemented using dSPACE DS1103 controller. A steady-state analysis has been developed for predicting the value of duty cycle as well as the reference current for maximum power point tracking at a given wind velocity or rotor speed of PMSG. Experiments have been carried out on a 48 V, 750 W, 500 rpm PMSG and the test results are furnished to validate the developed scheme.

In conventional arrangements of three-phase LLC converters, there are at least three magnetic components that occupy a considerable volume and mass of the power converter. Although, the three-phase LLC topology has many advantages over the single-phase one, circuit designers tend to select the single-phase topology because it has the minimal number of magnetic components. The purpose of this study is to reduce the number of the magnetic components of the three-phase topology, by integrating the three-discrete transformers into a single magnetic core, based on a theoretical framework. Lagrangian dynamics is applied to theoretically prove that it is possible to replace the three-discrete transformers by a single integrated transformer. The Lagrangian dynamics theory allowed us to derive a physically motivated model for the integrated transformer, in which each component of the integrated transformer has its own Lagrangian parameter. The Lagrangian model reveals that in a symmetrical design, there is no interphase coupling, and as a result the magnetic components can be downsized owing to the ac flux cancellation. Along with the theoretical discussion, the practical merits of implementing the integrated transformer is reported. Furthermore, the experimental tests are conducted utilizing a 500 W–390 V/12 V–200 kHz prototype.

Under unbalanced grid fault conditions, the current harmonic contents of a three-phase bidirectional AC/DC converter increase significantly and twice grid-frequency ripples exist in both active power and reactive power, which influence the output power quality of the converter. Compared with the conventional finite-state model predictive direct power control (MPDPC), the MPDPC with power compensation (MPDPC-PC) method is proposed for the three-phase bidirectional AC/DC power converter to reduce harmonic currents and output power ripples without extraction of complex positive/negative sequences from the grid voltage/current and phase-locked loop. The power compensation values are expressed by grid voltages and their quadrature signals that lag 90 electrical degrees in the αβ stationary coordinates system. MPDPC-PC exhibits better performance by reducing the harmonic contents of grid currents and eliminating active power or reactive power ripples of the three-phase bidirectional AC/DC converter with flexible reactive power compensation capability. Compared with the MPDPC and linear current control schemes, experimental results confirm the effectiveness of the designed method under unbalanced grid conditions.

Stator flux estimation for electrical machine using voltage model (VM) with a simple structure and the least parameters has been widely researched in high-performance drive systems. Existing low-pass filter (LPF)-based estimators either respond slowly or cannot adequately suppress DC drifts, thus, a vector transforming and signal filtering method using VM is proposed for flux estimation. An original flux vector is directly produced through a transformation for motor back electromotive force, and then, the desired flux is obtained through an optimised filter which is designed by combing LPF and band-pass filter with an optimal function. The proposed estimator can both eliminate DC drifts and obtain a fast response and high accuracy, and additionally, its structure is simplified by the decomposing process, which significantly reduces the computation and occupied resources. The effects of cut-off frequencies on dynamical responses and flux harmonics are investigated and the limitations are obtained. This estimator is applicable to extensive strategies, for instance, the implementation of a direct torque control-based electrical drive system is carried out. Theoretical analysis, simulation, and experiment are conducted to validate the feasibility and effectiveness of the proposed scheme.

This study proposes a technique that is able to improve the speed response of a four-phase DC–DC converter switching. The basic concept of the proposed technique is the inclusion of two shunt-connected voltage sources in series to the converter system. Using a higher input voltage to drive the load, a higher current per microsecond output system will be obtained and reverts to its nominal input upon obtaining desired references. Thus, the transient response observed when using this proposed technique is found to be much faster when compared to the conventional converter. Moreover, this technique is easily implemented as it requires only an additional voltage source, power switch, and power diode. The integrated model of the two shunt voltage-source in a four-phase DC–DC converter was simulated in MATLAB/Simulink and validated against the experimental results of a laboratory prototype, 600 W four-phase DC–DC converter. The novelty of this proposed technique is its ability to provide faster operations for critical loads applications, lower output capacitor and lower operating frequency.

This study introduces a new active-clamped current-fed push–pull dc–dc converter for renewable energy conversion applications. The proposed converter conserves small input current pulsation, high-voltage conversion ratio, zero-voltage switching (ZVS) and zero-current-switching operation for primary switches and rectifier diodes, respectively, over a large load range. Also, the additional active clamping circuit serves to suppress the voltage spike across all primary switches, as well as assists in achieving ZVS operation. So, the low-voltage switches with low on-state resistance can be adopted. These features can reduce switching loss, voltage stress, transformer turns ratio and diode reverse-recovery effect. More importantly, similar characteristics can be obtained with minimised switches compared with the reported converters that enable to reduce the cost and improve the reliability. Detailed steady-state operation, analysis, performance comparison, experimental results and loss breakdown of the proposed converter are fully discussed in this study. Finally, a 520 W prototype verifies the theoretical analysis.

This study proposes an input-voltage-sharing control scheme for use in input-series-output-series (ISOS) systems. An ISOS system consists of a set of closed-loop DC/DC converters. Each converter has a metal–oxide–semiconductor field-effect transistor (MOSFET) connected in parallel on the input side that is controlled by an input-voltage-sharing loop. The MOSFET works in the linear region to adjust the input power equilibrium. The proposed control scheme makes the closed-loop converters function as power devices that can be combined quickly and flexibly according to the specific voltage conversion requirements, which greatly shortens the time required to develop an ISOS system. The design principle of the input-voltage-sharing loop and the time and frequency domain simulation results are also provided in this study. A 600 W prototype composed of two DC/DC converters was built and employed to verify the steady state and dynamic characteristics of the proposed control scheme.

Three pulse-width-modulation (PWM) digital control approaches are evaluated to provide the current sharing between phases in high-power dual-interleaved DC–DC converters. The implementation of a digital peak current, multi-sample averaged current and an enhanced single-sample averaged current control in a TMS320F28377D is described. A summary of stability requirements is provided for designing the controllers and experimental results from a 60 kW, 75 kHz silicon carbide DC–DC converter are used to evaluate the steady-state and dynamic performance of the three control methods. Overall the best performance in terms of tracking and speed of response was achieved by the enhanced single-sample method. The multi-sampled technique provided the highest tracking accuracy, but at the expense of the slowest dynamic response. The fastest dynamic response was achieved by the digital peak current control, but this method is limited by poor noise immunity and instability for duty ratios in the region of 0.5.

Presently single stage boost multilevel inverters are becoming more popular for power conversion in renewable energy systems, AC–DC hybrid microgrids etc. Usually in these boost inverter the voltage stress across the inverter leg switches as well as current through these switches are quite higher as compared to load ratings which increases the chances of inverter leg switch failure. In this paper a three level voltage source boost inverter is proposed to achieve rated three level AC output voltage in a single power conversion stage. It retains all the advantages of three level quasi Z- Source inverter by using less number of passive components in the intermediate network between DC source and inverter leg. Beside the inherent shoot through fault tolerant feature the proposed inverter is capable to operate in open circuit failure to give rated balanced AC voltage at load. The above advantages of the proposed single stage inverter make it suitable for low and medium power renewable energy applications where size, weight are main constraint and some of the critical loads are connected to the system. The proposed inverter is verified by simulation (in MATLAB Simulink) and experiment with the help of a laboratory prototype.